The invention relates to a head-up display for vehicles, in which information from a display device is projected onto a transparent projection area. It is known from the prior art to transilluminate a liquid crystal display (LCD) as the display device and to display the light beams passing through the liquid crystal display on a transparent projection area, for example the front screen. Thus, the driver of a vehicle can receive information without having to avert his/her gaze from the traffic situation in front of his/her vehicle. The known liquid crystal displays have two transparent screens which are arranged at a distance and on which electrodes are arranged. A liquid crystal substance is arranged between the electrodes. A respective polarizer is applied on the external surfaces of the transparent screens. Provided that no voltage is present at two opposite electrodes, the direction of polarization of light beams which penetrate through the liquid crystal substance is rotated through 90 degrees. If a voltage is present at the electrodes, no rotation takes place when light penetrates through the liquid crystal substance. Provided that the directions of polarization of the two polarizers are rotated through 90 degrees, light can penetrate through the liquid crystal display if no voltage is present at the electrodes, since the plane of polarization of the light when penetrating through the liquid crystal substance is likewise rotated through 90 degrees. If a voltage is present, the direction of polarization of the light is not rotated, so that the light cannot penetrate through the second polarizer. It is known from the prior art, for example, for the liquid crystal displays to be embodied as dot matrix displays. Thus, information composed of individual pixels can be represented depending on the driving of the individual electrodes of the dot matrix display. The use of such known liquid crystal displays in a head-up display has the disadvantage that a very powerful light source has to be used, since, firstly, the brightness of the light on the transparent projection area must be great enough that the information can readily be perceived even in bright daylight, and the known liquid crystal displays allow only a small amount of light to pass through owing to the doubled light absorption by the two polarizers. It is thus necessary to provide a powerful light source, which consumes a large amount of energy and thereby produces undesirable heat which then has to be dissipated with a large outlay.
It is an object of the present invention, therefore, to specify a head-up display with a display device with a liquid crystal substance, in which the light source requires less energy. This object is achieved by virtue of the fact that the light which emerges from the liquid crystal substance is not sent through a polarizer, which is customary in a liquid crystal display, rather that the second polarization is effected by the reflection of the light, either at the transparent projection area or at one or more mirrors which are arranged in the beam path of the polarized light between the liquid crystal substance and the transparent projection area.
The transparent projection area may be part of the front screen of the vehicle or a separate screen arranged between the front screen and the driver.